Reduce CPU cycle on calling  TrafficStats for Rx and Tx bytes

TrafficStats get Rx or Tx bytes calls are CPU intensive calls.
Call TrafficStats API only once for each link layer stats for data stall
score report.

Bug: 230678224
Bug: 230380937

Test: atest FrameworksWifiTests
Change-Id: Id9782b7a22788e2f18ded7a58791de11a039afdb
8 files changed